Femur length, abbreviated FL, is a key biometric measurement obtained during obstetric ultrasound by measuring the ossified portion of the fetal femur from one end to the other. Along with the biparietal diameter, head circumference, and abdominal circumference, femur length is used in formulas to estimate gestational age and fetal weight. It is most commonly measured during the second and third trimesters. A short femur length can be a soft marker for chromosomal abnormalities or may indicate skeletal dysplasia, while a long femur length may suggest a constitutionally large fetus. Serial femur length measurements across multiple ultrasound examinations help track fetal growth over time.
Sonography Term